As devices such as mobile phone, digital AV apparatuses, IC cards etc. have been improved to have higher performance, semiconductor silicon chips (hereinafter, refer to as chips) to be mounted on the devices have to be smaller and thinner in order to greatly increase a number of chips mounted in packages of the devices. To greatly increase a number of chips mounted in the package, the chips should have a thin thickness in a range of 25 to 150 μm.
However, semiconductor wafers (hereinafter, refer to as wafers) to be substrates of the chips is weakened in strength when the wafers are polished to a thin thickness. The thin wafers with weak strength are easy to be cracked or curved. Moreover, the thin wafers with weak strength are difficult to transport by automatic transportation. This requires manual transportation, and thereby tedious handling.
To deal with this problem, a wafer support system has been developed to reinforce the strength of the wafers by adhering a plate (called a supporting plate, and generally made from glass or rigid plastic) to the wafers before polishing. The wafer support system prevents cracking and curving of the wafer. The wafer support system, which reinforces the strength of the wafers, allows automatic transportation of the thin semiconductor wafers.
The wafers and supports are adhered with each other via an adhesive tape, thermoplastic resin, an adhesive, or the like. After a wafer adhered with the supporting plate is thinned, the wafer is stripped off from the supporting plate before dicing. For example, in case where the wafer and the supporting plate are adhered with each other via an adhesive, the adhesive is dissolved so as to strip the wafer off from the supporting plate.
Conventionally, the dissolving the adhesive to strip the wafer from the supporting plate is time-consuming, for example, in permeating a solvent into the adhesive and in dissolving the adhesive. As a result, the stripping of the supporting plate from the wafer has been a long-time process. Patent Literature 1 discloses a method for using an adhesive allowing easy stripping so as to solve this problem.
In Patent Literature 1, it is described that works are adhered with each other via an adhesive including a first adhesive layer and a second adhesive layer on the first adhesive layer, the first adhesive layer including a first adhesive material in which thermally-soluble microcapsules are dispersed, the thermally-soluble microcapsules holding therein a releasing agent for reducing adhesiveness of the first adhesive material, and the second adhesive layer including a second adhesive material in which thermally expandable particles are dispersed.
Patent Literature 1 describes that, for the works adhered with each other via the adhesive, the stripping is carried out by heating the adhesive. The heating releases the releasing agent from the microcapsules into the first adhesive layer, and expands the thermally expandable particle. The expanding applies a pushing force to cause a crack between the first and second adhesive layers. As a result, the stripping can be carried out without leaving residuals of the adhesive on the works.